📦(helm) add support for specifying an existing secretName

[PascalCompiles]

Purpose

This pull request adds support for specifying a custom secretName within the Ingress configuration. This update makes the find chart consistent with how TLS secrets are handled across other La Suite numérique Helm charts.

• Behavior Context: This configuration alignment follows the convention outlined in the docs helm chart README.md under ingress.tls.secretName.
• Code Reference: The default/override logic is lifted directly from the docs helm chart here.

Proposal

• Update templates/ingress.yaml to prioritize .Values.ingress.tls.secretName if provided, falling back to {{ $fullName }}-tls by default.
• Add ingress.tls.secretName: null to values.yaml for clear user visibility.
• Update the find helm chart README.md.
• Bump helm chart version.